I think you are referring to savings syns and not flexisynning though.
I take my full 15 syns a day, I add them up to 105 syns a week. I have been known to use 40 in one day and then spread the 65 other the others 6 days which has still given me 10 syns a day. I still consistently lose 2lbs a week doing this. Although agree that just because it works for me, does not mean it will work for everyone.
The way I see it is 105 syns is the same amount of calories over the week whether you spread them out or have more in one day. Having the flexibility to use more in one helps me stick to plan as it allows me treats when I am craving which I otherwise could not have.